That statement goes beyond what Washington law actually says.
RCW 59.18.210 states (for residential tenancies) that
Tenancies from year to year are hereby abolished except when the same
are created by express written contract. Leases may be in writing or
print, or partly in writing and partly in print, and shall be legal
and valid for any term or period not exceeding one year, without
acknowledgment, witnesses or seals
In Washington, a supposedly multi-year lease which is not notarized is converted into a month-to-month lease. This is in distinction to mobile home lot leases (RCW 59.20.050) which allow terms of more than one year. There is no requirement to attach a legal description of the property, which would be meaningless for an apartment built on a particular land parcel (hundreds of rental units may exist on a parcel with a specific legal description).
A detailed analysis of a "legal description" that is to be included in records of survey for land surveyor is set forth here by the AG, given RCW 58.09.060, who notes that it is not defined under the law, and instead
we conclude that the "legal description" required by the statute is
simply that description of a tract of real property which is
sufficient to meet the requirements of a valid deed of conveyance
under the long-standing provisions of RCW 64.04.010; i.e.,". . . a
description of land sufficiently definite to locate it without
recourse to oral testimony, . . ."
citing various kinds of technical measurements that could be used to record the boundaries of real property.